Computational Optimization of Internal Combustion Engines

332 Pages·2012·10.46 MB·English

Computational Optimization of Internal
Combustion Engines

Yu Shi Hai-Wen Ge Rolf D. Reitz
• •
Computational Optimization
of Internal Combustion
Engines
123
Dr. YuShi Prof.RolfD.Reitz
Department of Chemical Engineering EngineResearch Center
Massachusetts Instituteof Technology Universityof Wisconsin-Madison
Bldg.66-264 1500EngineeringDr.
77Massachusetts Avenue Madison, WI53706
Cambridge,MA 02139 USA
USA e-mail: [email protected]
e-mail: [email protected]
Dr. Hai-Wen Ge
EngineResearch Center
Universityof Wisconsin-Madison
1500EngineeringDr.
Madison, WI53706
USA
e-mail: [email protected]
ISBN978-0-85729-618-4 e-ISBN978-0-85729-619-1
DOI10.1007/978-0-85729-619-1
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Preface
Striking progress has been made in internal combustion engine design due to the
development of computer models and optimization techniques. In this book we
strive to document the state of the art in predictive IC engine modeling and
optimization.Thefactthatthisisanimportanttopicforresearchanddevelopment
is emphasized by society’s reliance on IC engines for transportation, commerce
andpowergeneration. Indeed, theworldasweknow it wouldbe aquite different
place were it not for the remarkable internal combustion engine! It drives all
manner of utility devices (e.g., pumps, mowers, chain-saws, portable generators,
etc.), as well as earth-moving equipment, tractors, propeller aircraft, ocean liners
and ships, personal watercraft and motorcycles. However, its major application is
powering the 600 million passenger cars and other vehicles on our roads today.
250millionvehicles(cars,buses,andtrucks)wereregisteredin2008intheUnited
States alone. According to the International Organization of Motor Vehicle
Manufacturers,about50millioncarsweremadeworld-widein2009,comparedto
40 million in 2000. Much of this dramatic increase comes from increased pros-
perity in China, which became the world’s second-largest car market in 2010. A
third of all cars are produced in the European Union, and about 50% of those are
powered by diesel engines. Thus, IC engine research spans both gasoline and
diesel powerplants.
The world’s economic expansion has been powered by cheap oil. It has been
argued that the increasein population from 1.9 billion inthe 1920s totoday’s 6.6
billion has been made possible, in part, by fossil fuel combustion and by the Ha-
ber–Boschprocesstomakecropfertilizer.80%oftheroughly80billionbarrelsof
crude oil consumed annually world-wide is used in IC engines for transportation.
IntheUnitedStates,10millionbarrelsofoilareusedperdayinautomobilesand
light-duty trucks, and 4 million barrels per day are used in diesel engines, with
totaloilusageofabout2.5gallonsperdayperperson.Ofthis,62%isimportedoil,
which at today’s $80/barrel, costs the US economy $1 billion/day. This cost is
certain to increase as more-and-more economic development drives increased de-
mand for automotive fuels world-wide.
v
vi Preface
Associatedwithourmassiveoiluseistheaccompanyingannualemissionof37
billion tons of CO (6 tons each for each person in the world) and other pollutant
2
emissions, including nitric oxides (NOx) and particulates (soot). Pollutant emis-
sions have serious environmental and health implications, and thus most govern-
ments have imposed stringent vehicle emissions regulations that are continually
being tightened further. In addition, CO emissions contribute to Green House
2
Gases (GHG), which some fear could lead to climate change with unpredictable
consequences. Drastic reductions in fuel usage will be required to make appre-
ciable changes in GHG trends.
Today’s gasoline IC engine powered vehicle equipped with its 3-way catalyst
foremissioncontrolconvertsonlyabout16%ofthechemicalenergyinthefuelto
useful work—the rest is lost to the environment. The modern automotive diesel
engine is 20 to 40% more efficient than its gasoline counterpart. However, mea-
sures introduced to meet emissions mandates, such as the use of non-optimal fuel
injectiontimings,largeamountsofExhaustGasRecirculation(EGR)orultra-high
injectionpressures reduce dieselenginefuelefficiencies,andalsoincreaseengine
expense.ManydieselenginemanufacturershaveelectedtouseSelectiveCatalytic
Reduction (SCR) exhaust after-treatment for NOx reduction. However, with SCR
thereisalsoafuelpenaltysinceareducingagentsuchasurea(carbamide)mustbe
sprayedintotheexhauststreamatrates(andcost)ofabout1%ofthefuelflowrate
forevery1g/kWhofNOxreductiondesired.SootcontrolisachievedusingDiesel
Particulate Filters (DPF), which generally require periodic regeneration. This is
achieved by adjusting the fuel-air mixture strength so as to increase exhaust
temperatures to burn off the accumulated soot, which imposes as much as a 3%
additional fuel penalty.
From thesediscussions it is clear that new technologies are urgently needed to
improve the efficiency of both gasoline and diesel engines. For further improve-
ments, engines need to be optimized to balance emissions, fuel cost, and market
competitiveness. As described in this book, this task can be efficiently attacked
using state-of-the-art computational models and optimization methods. This has
been made possible, in part, by dramatic increases in computer speeds that have
increased 10,000-fold in the past 15 years. Engine development is now greatly
facilitatedusingmulti-dimensionalComputationalFluidDynamic(CFD)toolsand
optimization algorithms, supported by significantly reduced requirements for ex-
perimental testing, which is extremely expensive.
An additional enabling factor for engine CFD modeling has been the devel-
opment of predictive models for the physical processes occurring in the com-
bustion chamber. Many of these models are reviewed in this book, together with
discussion of strategies to reduce computational cost and numerical inaccuracies.
Exampleapplicationsarepresentedfortheoptimizationof2-strokespark-ignition
gasoline and 4-stroke heavy- and light-duty diesel engines. The effects of design
parameters including nozzle design, injection timing and pressure, swirl, EGR,
engine size scaling, and piston bowl shape are considered, together with explo-
ration of fuel effects for low temperature combustion strategies. It is also dem-
onstrated how optimization results can be used in combination with regression
Preface vii
analysis to explore and explain the complex interactions between engine design
parameters.
The present example applications also demonstrate that current multi-dimen-
sional CFD tools are mature enough to guide the development of more efficient
and cleaner internal combustion engines. New low temperature combustion con-
cepts, such as Homogeneous Charge Compression Ignition (HCCI), Premixed
Charge Compression Ignition (PCCI) and Reactivity Controlled Compression
Ignition (RCCI) offer the promise of dramatically improved engine efficiencies.
For example, optimized dual fuel RCCI operation (port injection of gasoline
togetherwithoptimizedin-cylindermultipledieselfuelinjections)wasdiscovered
with computer simulations using the models and tools described in this book
(Kokjohn et al. 2009). The computer simulations predicted high-efficiency, low-
emissions operation with excellent combustion phasing control at high and low
engine loads without excessive rates of pressure rise. Subsequent engine experi-
mentshaveconfirmedthemodelpredictions,andhavedemonstratedthatUSEPA
2010 NOx and soot emissions mandates can be met in-cylinder without after-
treatment,whileachievingupto57%grossindicatedthermalefficiency(Kokjohn
et al. 2011).
The adoption of RCCI combustion engines could improve fuel efficiencies by
up to 20% over standard diesel operation, while also providing dramatic cost
reductionsthroughtheeliminationoftheneedforexhaustafter-treatment.RCCIis
applicable with a wide range offuels, including conventional gasoline and diesel,
aswellasbiofuelssuchasethanolandbiodieselandtheirblends.Theimplications
ofsuchimprovementsinfuelefficiencyareverysignificant.Forexample,ifRCCI
were adopted to replace the relatively inefficient spark-ignition engine it is esti-
mated that US transportation oil usage could be reduced by 34%, which equals
100% of the current US oil imports from Persian Gulf. If these efficiency
improvements were combined with electric hybrid technologies in the vehicle,
even greater reductions in oil usage would be possible.
The ultimate goal of engine modeling is to guide designers to improve engine
performanceandtoreducepollutantemissions.Thegoalofthisbookistoprovide
an up-to-date reference to current developments and future directions in the field
ofenginemodeling. We hopethatyouwillthinkthatwehave achieved thisgoal.

Acknowledgments
This book expands on recent computational optimization studies of internal com-
bustion engines performed at the Engine Research Center of the University of
Wisconsin-Madison. The present work would not have been possible without the
solidresearchfoundationthatourERCcolleagueshavebuiltoverthepastdec-ades.
Wewouldliketoexpressoursinceregratitude tothem.Duringthepreparationof
this book, we also received valuable suggestions from our colleagues, Dr. Shiyou
Yang, Dr. Yuxin Zhang and Mr. Yue Wang, towhom we are indebted.
The work included in this book was supported financially by several govern-
ment and industry research projects. We are grateful to the US Department of
Energy, Caterpillar Inc., Ford Motor Company, General Motors, and Detroit
DieselCompanyfortheirlongtermsupport.WealsothankDr.DavidWickmanof
Wisconsin Engine Research Consultants for allowing use of the Kwickgrid soft-
ware. ESTECO provided access to optimization software (modeFRONTIER),
which facilitated some of the assessment studies in this book.
We thank the Society of Automotive Engineers (SAE), American Society of
Mechanical Engineers (ASME), American Chemical Society (ACS), SAGE Pub-
lications Ltd., Elsevier, and Taylor & Francis for allowing us to use figures and
other materials from previously published articles. We also thank Springer for
inviting us to write and helping us to prepare this book.
Finally, we very much appreciate our families for their love, encouragement,
support, and their understanding in our lives, in our research work, and in the
preparation of this book.
December 31, 2010 Yu Shi
Hai-Wen Ge
Rolf D. Reitz
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